In order for metallocenes to be particularly useful in slurry type polymerization processes, it has generally been found necessary to form a catalyst system in which the metallocene and the cocatalyst are insoluble during the polymerization. Various approaches have been taken to provide insoluble heterogeneous catalyst systems that would be applicable. One technique involves the employment of metallocenes containing unsaturated substituents which can be prepolymerized in the presence of a cocatalyst to produce a solid insoluble catalyst system. An example of such a process is disclosed in U.S. Pat. No. 5,498,581.
Another approach for preparing such an insoluble heterogeneous catalyst system involves the employment of a special type of metallocene referred to as a metallocycle metallocene. A metallocycle type metallocene is one in which one of the cyclic dienyl groups that is pi bonded to the metal of the metallocene also contains a substituent which is also bonded to the metal of the metallocene. An example of such a metallocene is disclosed in U.S. Pat. No. 5,654,454. In that case, the metallocycle was produced by a hydrozirconation type reaction. Such compounds are referred to as metallocycles for the reason that there is what can be viewed as a cyclic structure comprising the cyclic dienyl group pi bonded to the zirconium and the substituent on the cyclic dienyl group being also bonded to the metal. It is believed that such compounds form self supported catalyst systems as a result of repeated ethylene insertions into the metal-substituent bond to result in a prepolymer having pendant metallocene groups.
An object of the present invention is to provide a new catalyst system comprising the product resulting from the combination of a cocatalyst and a metallocycle metallocene produced from a metallocene having an arylalkyl substituent on at least one of the cyclic dienyl groups of the metallocene by reacting the metallocene with two equivalents of an alkali metal alkyl.
Another object of the present invention is to provide a process for producing polymers from olefins comprising contacting an olefin with such a catalyst system under polymerization conditions.
Still another object of the present invention is provide a halogen-free metallocene capable of use as an olefin polymerization catalyst.